.

Thursday, June 22, 2006

42n-1

How did the Universe begin? Many scientists would regard this as one of the most profound questions of all. But to Stephen Hawking, who has perhaps come closer than anyone to answering it, the question doesn't in fact even exist.

Hawking and Thomas Hertog are about to publish a paper claiming that the Universe had no unique beginning. Instead, they argue, it began in just about every way imaginable (and maybe some that aren't).

That, they insist, is the only possible conclusion if we are to take quantum physics seriously. "Quantum mechanics forbids a single history," says Hertog.

Thomas Hertog and Hawking call their theory 'top-down' cosmology, because instead of looking for some fundamental set of initial physical laws under which our Universe unfolded, it starts 'at the top', with what we see today, and works backwards to see what the initial set of possibilities might have been. In effect, says Hertog, the present 'selects' the past.

Within just a few seconds after the Big Bang, a single history had already come to dominate the Universe, he explains. So from the 'classical' viewpoint of big objects such as stars and galaxies, things happened only one way after that point. Other 'histories', say, one in which the Earth formed only 4,000 years ago, have made no significant contribution to this cosmic evolution.

But in the first instants of the Big Bang, there existed a superposition of ever more different versions of the Universe, instead of a unique history. And most crucially, Hertog says that "our current Universe has features frozen in from this early quantum mixture". http://www.nature.com/news/2006/060619/full/060619-6.html